Packaged meat products include beef, pork, poultry, mutton, lamb, veal, fish, and other types of meats that are packaged for retail sale to consumers. Many food retailers no longer have in-house butchers that cut and wrap fresh meat products, but rather the fresh meat products are packaged by meat processors in case-ready packages and then shipped to the food retailers. In general, the meat processors strive to package the meat products in a manner that maintains the freshness of the meats for a significant period of time to provide a longer shelf life. Case-ready packages for the meat products, for example, should maintain the color of the meat product, inhibit odors, and retard microbial activity. The packages for the meat products should also enable consumers to view the meat.
One type of package, called “over-wrap” or “tray-wrapped” packages, has a shallow tray (e.g., a Styrofoam tray) and a gas permeable elastomeric film over-wrapped around the shallow tray. Over-wrapped packages accordingly allow oxygen and other gases to transfer into and/or out of the package. Although oxygen initially causes the meat product to be bright red or have another suitable color, over time oxygen degrades the color and flavor of the meat. Over-wrapped packages produced at central case ready facilities, therefore, have a limited shelf life and are not well suited for many retail applications.
Another type of package, called “lid stock” packaging, includes a plastic tray with an upper peripheral edge and an elastomeric film sealed to the upper peripheral edge. The plastic tray and the elastomeric film are often formed of materials having low gas permeabilities to substantially inhibit or even prevent gases from transferring into and/or out of the package. Many lid stock packages also have a modified atmosphere to maintain the color of the meat product and/or retard microbial activity to prolong the shelf life of the packaged meat product. In such Modified-Atmosphere Packages (MAPs), the air is evacuated from the packages within a chamber using a vacuum, and then the evacuated packages are back-flushed with a controlled-composition gas before sealing the elastomeric film to the plastic tray. In high-oxygen MAPs, one approach uses a controlled-gas composition including about 80% oxygen and about 20% carbon dioxide. Low-Oxygen MAPs are another approach that essentially exclude oxygen and instead use about 80-20% carbon dioxide and about 20-80% nitrogen (e.g., about 65% N2 to about 35% CO2). High-oxygen MAPs can significantly extend the shelf life of the packaged meat product compared to over-wrapped packages, but unfortunately the color of the meat still tends to change over time in a manner that renders the meat product less attractive to consumers. For example, ground beef and other red meats may have a suitable red color when they are first packaged in an impermeable MAP, but they gradually develop a less attractive appearance over a number of days (e.g., 10-12 days). Moreover, even if the meat maintains a suitable color, microbial activity can develop a sour odor in the package and eventually render the meat inedible.
One concern with high-oxygen MAPs is that the package itself is relatively large compared to the size of the meat product to provide sufficient headspace for the volume of the controlled-composition gas within the MAP. It is widely understood that a relatively high-volume headspace is necessary in an oxygen-based MAP because the container is impermeable and must contain a sufficient amount of oxygen to maintain an attractive red color on the meat product for a commercially acceptable shelf life. In particular, common wisdom teaches that the volume of the headspace (i.e., gas volume) should be at least as great as the volume of the meat in the container. Common commercial practice teaches that the gas-to-meat volume ratio (gas:meat ratio) should be at least about 1.5:1 with recommended ratios of 2.5:1 to 3.0:1 or even higher. At lower gas:meat ratios, research indicates that the meat will develop an unattractive color in 15 days or less. See C. O. Gill, “Extending the Storage Life of Raw Chilled Meats,” Meat Science, 43, pp. S99-S108 (1996); Y. Zhao, J. H. Welles, and K. W. McMillin, “Dynamic Changes of Headspace Gases in CO2 and N2 Packaged Fresh Beef,” Journal of Food Science, 60(3), 571-576 (1995). The entirety of each of these references is incorporated herein by reference. As a result of the large headspace in high-oxygen MAPs, these packages occupy a significant volume in costly refrigeration units in which the packaged meat products are stored, shipped, and displayed. This increases the cost for storing, shipping, and displaying the meat products. The large headspace may also provoke a negative consumer perception of the meat products.
Still another type of packaged meat product includes a plurality of over-wrapped meat packages or other types of gas permeable packages contained in a gas impermeable secondary container flushed with a mixture of gases (e.g., oxygen, carbon monoxide, carbon dioxide, and/or nitrogen). Although the secondary container is impermeable and has a modified atmosphere, each of the individual packages containing the meat products is permeable to gases. Retailers are advised to remove the individual packages from the secondary container within a stated distribution period, and then display the individual packages for retail sale for a defined retail period of time after the individual packages have been removed from the secondary container. The shelf life of the individual packages is limited after they have been removed from the secondary container because the individual packages are permeable to oxygen. Therefore, this packaging suffers from concerns similar to those of over-wrapped packaging.
Still another type of packaging provides a plastic tray and a two-ply cover having a gas permeable film attached to the upper rim of the tray and a gas impermeable film attached to the gas permeable film. The container holds a meat product and has a modified atmosphere while the gas impermeable film is attached to the gas permeable film. At the retailer, the retailer removes the gas impermeable film from the gas permeable film, allowing oxygen and other gases to pass into and out of the container while it is displayed for sale. This container accordingly has a limited shelf life as well.
Still another container design is a low-oxygen container in which the meat product is packaged in an atmosphere having less than 0.5% carbon monoxide (CO) and the balance a mixture of carbon dioxide (CO2) and/or nitrogen (N2). In particular, research in Norway indicates that suitable levels of carbon monoxide in such modified atmospheres are from 0.1-0.5%. A common gas composition for packaging red meats in these containers contains approximately 0.4% CO and a mixture of CO2 and N2 for the balance. The gas:meat volume ratio of these packages, however, is believed to have been approximately the same as that of the high-oxygen packages described above (e.g., at least as great as the volume of the meat in the container, or more in line with commercial practices of gas:meat volume ratios of at least about 1.5:1 and more commonly 2.5-3:1 or higher). Therefore, the total volume of these packages also inefficiently uses the available space for storing, shipping, and displaying the packaged meat products.